Many factors contribute to the formation of saccular aneurysms, particularly neural aneurysms. One of the major contributors is wall shear stress (WSS), which in addition to hypertension leads to a reduction in the elastic tissue of the tunica media, thereby contributing to the formation of the aneurysm. The effect of wall shear stress is heightened at certain anatomical geometries such as bifurcations, for instance at the point where the basilar artery (BA) divides into the posterior cerebral arteries (PCA).
It is known to try to treat aneurysms by filling the aneurysm sac with a filler such as a prosthetic coil. The methodology behind the use of prosthetic coils is to establish a hard thrombus formation within the sac as a means of isolating the aneurysm wall from the flow of blood. While this can be effective in the treatment of many types of aneurysm, it is less effective when the aneurysm occurs at a bifurcation or trifurcation, such as at the base of the basilar artery.
It is also known to close off the entrance to the aneurysm sac or to divert the flow of fluid therefrom, but known devices are not always optimal and in general not always suitable for treatment of aneurysms at vascular bifurcations.
Examples of devices for treating aneurysms can be found in WO-2010/085344, U.S. Pat. No. 6,309,367, U.S. Pat. No. 6,613,074, US-2006/0200234, US-2007/0088387, US-2009/0228029 and US-2011/022149.